Fine pattern formation is carried out by the photolithography in manufacturing processes of a semiconductor device. A number of substrates called transfer masks are normally used for this fine pattern formation. The transfer mask comprises generally a transparent glass substrate having thereon a fine pattern made of a metal thin film or the like. The photolithography is used also in the manufacture of the transfer mask.
In the manufacture of a transfer mask by the photolithography, use is made of a mask blank having a thin film (e.g. a light-shielding film or the like) for forming a transfer pattern (mask pattern) on a transparent substrate such as a glass substrate. The manufacture of the transfer mask using the mask blank is carried out by forming a required fine pattern in a resist film coated on the mask blank and etching the thin film according to the resist pattern. Therefore, the properties of the thin film formed in the mask blank as an intermediate product almost exactly determine the performance of the transfer mask.
In recent years, the miniaturization of patterns has advanced more and more and, following it, the wavelength of an exposure light source for use has been shortened from a KrF excimer laser (wavelength 248 nm) to an ArF excimer laser (wavelength 193 nm). The miniaturization of transfer patterns is also significant. Patent Document 1 points out that a reduction in the thickness of a resist film is necessary for dealing with the miniaturization of a transfer pattern. It further describes that since a material composed mainly of chromium, which has conventionally been used as a transfer-pattern thin film, is dry-etched with a chlorine-based gas containing oxygen, a resist pattern also tends to be damaged during the etching and thus that it is difficult to reduce the thickness of the resist. Taking this into account, it proposes a laminated structure in which tantalum or molybdenum silicide that can be dry-etched with a fluorine-based gas is used as a material of a transfer-pattern thin film adapted to be capable of dealing with the reduction in the thickness of the resist and in which there is further provided a thin film of chromium or the like having high etching selectivity against the fluorine-based gas, i.e. a so-called hard mask film. By the use of this laminated structure, pattern transfer to the transfer-pattern thin film can be carried out by dry etching using the hard mask film as a mask and, therefore, it is sufficient for the thickness of the resist film to be large enough to carry out pattern transfer to the hard mask film. By the use of such a laminated structure of the thin film for transfer pattern formation and the hard mask film, the thickness of the resist can be more reduced than the case of direct transfer to the thin film composed mainly of chromium using the resist film as a mask and, therefore, the effect is obtained to some degree.
On the other hand, in a halftone phase shift mask blank, a material containing a metal silicide, such as a MoSiOC film described in Patent Document 2, has hitherto been widely used as a phase shift film which is a film for forming a transfer pattern in the manufacture of a mask. On the other hand, in a transfer mask, the in-plane dimensional uniformity of a transfer pattern is important for obtaining a required transfer result on a wafer. According to Roadmap ITRS 2008 updade published by the International Semiconductor Roadmap Committee, the dimensional uniformity of a mask pattern is required to be 2.0 nm or less in the mask plane in the lithography of less than 45 nm DRAM half-pitch.